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The mechanics of valve cooling in internal-combustion engines. Investigation into the effect of VSI on the heat flow from valves towards the cooling jacket.

By Yahia Abdel-Fattah

Abstract

Controlling the temperature of the exhaust valves is paramount for proper\ud functioning of engines and for the long lifespan of valve train components. The\ud majority of the heat outflow from the valve takes place along the valve-seat-cylinder\ud head-coolant thermal path which is significantly influenced by the thermal contact\ud resistance (TCR) present at the valve/seat and seat/head interfaces.\ud A test rig facility and experimental procedure were successfully developed to assess\ud the effect of the valve/seat and seat/head interfaces on heat outflow from the valve,\ud in particular the effects of the valve/seat interface geometry, seat insert assembly\ud method, i.e. press or shrink fit, and seat insert metallic coating on the operating\ud temperature of the valve.\ud The results of tests have shown that the degree of the valve-seat geometric\ud conformity is more significant than the thermal conductivity of the insert: for low\ud conforming assemblies, the mean valve head temperature recorded during tests on\ud copper-infiltrated insert seats was higher than that recorded during tests on noninfiltrated\ud seats of higher conformance.\ud The effect of the insert-cylinder head assembly method, i.e. shrink-fitted versus\ud press-fitted inserts, has proved negligible: results have shown insignificant valve\ud head temperature variations, for both tin-coated and uncoated inserts. On the other\ud hand, coating the seat inserts with a layer of tin (20-22¿m) reduced the mean valve\ud head temperature by approximately 15°C as measured during tests on uncoated seats.\ud The analysis of the valve/seat and seat/head interfaces has indicated that the surface\ud asperities of the softer metal in contact would undergo plastic deformation. Suitable\ud thermal contact conductance (TCC) models, available in the public domain, were\ud used to evaluate the conductance for the valve/seat and seat/cylinder head interfaces.\ud Finally, a FE thermal model of the test rig has been developed with a view to assess\ud the quality of the calculated TCC values for the valve/seat and seat/head interfaces.\ud The results of the thermal analysis have shown that predicted temperatures at chosen\ud control points agree with those measured during tests on thermometric seats with an\ud acceptable level of accuracy, proving the effectiveness of the used TCC models.Full text access was made available at end of embargo period: Jan 1st 2013

Topics: Engine valve cooling, Thermal interfaces, Valve / seat thermal conductance, Seat / cylinder head thermal conductance, Heat flow analysis, Finite Element, Exhaust valves, Internal-combustion engine
Publisher: School of Engineering Design and Technology
Year: 2009
OAI identifier: oai:bradscholars.brad.ac.uk:10454/4333
Provided by: Bradford Scholars
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